Gaseous conduction apparatus



Oct. '17, 1933. P. L. SPENCER GASEOUS CONDUCTION APPARATUS Filed Aug.24, 1928 w T m W l M TTOQNEY Patented l 1,991,299 GASEOUS CONDUCTIONarraaa'rus Percy; L. Spencer, Medford, Mass.,-assignor to Baytheon,Inc., Cambridge, Mass., at corporation of Massachusetts ApplicationAugust 24, 1929. Serial no. 901,99

1 Claim. (01. 250-215) My invention relates to gaseous conductionapparatus and particularly to improvements in rectifiers of the gaseousconductiontype. Rectifiers of this type have been known and used to 6 alarge extent. The type of rectifier to which my invention pertains isparticularly characterized by the fact that the electrodes are ingeneral non-thermionic. Such rectifiers have ordinarily been used incircuits where the voltage was 300 or less between cathode and anode.Although this type of rectifier may, and very often does, successfullyrectify higher voltages, such rectification is ordinarily beyond thecapacity of the tube and generally results in greatly shortened life.For many purposes it is highly desirable that voltages up toseveralthousand be successfully rectified. The simplicity of mechanicalconstruction, ease of starting and operation, and efilciency of thistype of rectifier make it highly suitable for pur- 20 poses wherecurrents under one ampere are required. My invention aims at soimproving the gas type of rectifier that it will successfully withstandvoltages of 2000 without losing its unilateral conductivity.

In gaseous conduction devices it is well known that an increase in thepressure of gas used results in a heavier discharge current and lowerpotential drop across the electrodes. n the other hand, such highpressure is accompanied by low resistance to back voltage. This isbecause with a given electrode spacing, a high pressure gas has on theaverage more gas particles in the inter-electrode space to be ionized byelectrons from the cathode. Such ionization results in acumulative'buildin'g up of a heavy discharge.

In order to obtain desirable insulating characteristics for reversepotential, a tenuous and highly rarefied atmosphere is desirable. By myinvention, I am enabled to combine in. one tube the advantages of thepresence of a gas at high pressure between electrodes when dischargeocours and a low pressure between electrodes on member from ionicbombardment. This shield reverse potential. By thus combining these twofeatures, advantages inure to the tube to give it highly desirablecharacteristics.

An additional feature of my invention resides in the construction of thecontainer, especially near the seals. The proximity of the region ofdischarge to seals results in raising the temperature of the glass atthose points so that suflicient conductivity to result in electrolysisat the seals,

is brought about. Furthermore, the mass of glass at the seals, as wellas the presence of metal, renders it highly desirable that they be keptcool.

552 'By my construction, the container is-so shaped that the seals areprotected from any undesirable action.

In general my invention comprises an insulating vessel in'which are atleast two electrodes spaced apart from each other in an atmosphere 6 ofsome gas, preferably of the rare group, such ashelium. The anode may beof any shape whatsoever and preferably is so shaped that it presents arelatively small amount of active surface. Spaced apart from this anodeis a cathode. The spacing between the cathode and anode should not betoo great because the starting voltage as well as voltage drop becomeundesirably high. 0n the other hand, the spacing should not be too smallbecause the gas pressure in the tube as a whole is low and hence, butlittle current could pass through the tube. The cathode is a thin memberand has a concave active surface and preferably such a surface as mightbe formed by revolving any plane figure about an axis.

The anode may be constructed of iron, carbon, tantalum or any othersuitable material. The cathode may be of suitable refractory material,the active surface of which is treated in such manner that it has a low.work function. Preferably the cathode consists of a thin sheet oftantalum which has been specially treated. The active surface of thetantalum iscoated with solutions of nitrates of various metals of thealkali and'alkaline earth group, such as barium and strontium. Thesenitrates are thereafter burned into the tantalum by an intense flame.This process is repeated several times causing the tantalum to becomesomewhat brittle and assume a whitish and crusted appearance. Cathodestreated in this manner have been found to be very eflicient anddesirable, not only in this tube but in othertubes as well. The cathodeand process of makingit is claimed in a copending case of mine, SerialNo. 289,845, filed Ju1y2,1928. The anode-is preferably protected by ashield member of metal actsnot only to protect the anode, but also theextreme edges of the insulation around the anode. A shield also protectsthe cathode insulator. 1

The seals are protected from harmful influences by causing the containerto assume a 1'9. entrant shape-near the seals. An insulator fills 105 upthe space adjacent the seal on the inside. The glass surface near theseal is so extended that there-is little possibility of the seal,becoming hot. i

Electrons emerging from the surface of a 9 repulsion go off in alldirections.

cathode leave itin a generally normal direction. It is obvious thatspace charge due to other electrons as well'as the direction of theelectrostatic gradient may change in some degree the angle of emission.Electrons leaving the entire surface'of the cathode as disclosed here,in this general way will tend to meet in a region along the axis of theconcave surface of the cathode. This focal region in a geometrical sensemay be anything from a point to a solid region depending upon the shapeof the active surface. The actual electronic focal region can never bevery sharp because of the tremendous repulsion between electrons.Electrons in going to the focal region cause ionization. 4 Both theelectrons and ions will congregate in the focal region resulting in adense conglomeration of electrons and ions. Such a condition will makefor more intense ionization by electrons coming from the cathode. Theelectrostatic gradient will draw the electrons to the anode. Since thefocal region is a region of intense ionization, a copious supply ofelectrons is assured and a heavier current will be passed through thetube.

Electrons in leaving the cathode surface and traveling toward the focalregion have a tendency to push all gas particles and ions, which theyencounter, into the focal region, thus setting up a region ofcomparatively high pressure there. As stated above, this is conducive tothe establishment of a heavy current through the tube.

On reverse potential any electrons leaving the anode surface are notfocused and due to their Most of the electrons are, therefore, renderedharmless and useless as far as initiating a reverse discharge isconcerned.

Furthermore, whatever ionization may occur is scattered and ineffective.This is equivalent to having a gas at very low pressure on reversepotential.

A tube of this character has been found to rectify a current of over aquarter of an ampere' at 2,000 volts.

In operation, the tube is characterized by a luminescence which isglow-like as far as characteristics are concerned. When starting underno load or very light load, the tube exhibits a diffused glow extendingbeyond the confines of the inter-electrode space. This glow is most1ntense at the center in the space between the cathode and anode. Thisintense spot is generally located well within the concave active surfaceof the cathode and appears to be distinct therefrom. As the load isincreased, the diffused portion of the glow appears to shrink while theintense portion enlarges. At the same time this intense portion of theglow comes closer toward the anode along the axis of the cathode. Atfull load the entire discharge through the tube is concentrated in anintense ball of fire between the cathode and anode and distinct fromboth. There is little or no glow visible out- The drawing shows asectional view of a tube embodying my invention, the tube beingapproximately one half size.

A container 1 of glass or any other insulating material has elongatedends 2 with reentrant portions 3 and 4. There is thus a considerablecooling surface near the seals, keeping them cool. Mounted in portions 4are insulators 5 of any suitable material such as lava or the like.Theseinsulators may be disposed in any suitable manner and arepreferably so disposed as to fill up and snugly lit the space withinportions 4. Passing through the center of one of insulators 5 in ananode 6 of any suitable material. At one end of the anode is connected alead wire 17 suitably sealed as it passes through the glass. Anode 6projects a short distance beyond the end of insulator 5. Within acircular groove 7 around insulator 5 and near one end thereof, isretained an outer shield member 8 and an inner shield member 9. Outermember 8 has-a hole 10 which is slightly larger than the diameter ofanode 6. Inner shield 9 has its edge adjacent the anode bent over sothat the edge forms a hole somewhat larger than anode 6. Anode 6preferably is disposed with its end below the hole 10 of shield 8 and alittle 'above the upturned edge of inner shield 9. 4

Through other insulator 5, lead 18 suitably sealed where it comesthrough the glass, emerges beyond the insulator and supports a cathode15. This insulator also has a groove 7 supporting a shield member 11.The cathode may be supported on the wire in any su table way, as bywelding. As shown here, the cathode consists of a conical member, theinner surface of which a has been rendered active as previously stated.

However, the shape of the cathode is not restricted to that of a cone.The cathode may be ellipsoidal, parabaloidal, or any other desirableshape. The distance between the tip of anode 6 and cathode 15 is suchthat anode 6 is substantially at the tip of cone 15 reversed. Anode 6 isat the axis as shown. However, if more than one anode is to be used,they may be placed within a short distance of each other and occupyingapproximately corresponding positions.

The tube is exhausted in accordance with usual practice and theelectrodes are freed of occluded gases. Thereafter, any gas at a lowpressure is introduced within the vessel. Preferably helium at apressure of about 6 m. m. is used.

When the tube operates, it is evident that the portions of the glassstem nearest the region. of discharge protect the seals. By making thestems reentrant, a large surface is exposed to the air allowing the heatto be dissipated and keeping the seals cool.

What is claimed,

A unidirectional gaseous discharge tube of the type wherein thedischarge .is initiated in the form of a glow, comprising an evacuateden-

